The repercussions of King's decision are not yet known, but this may well have been the Islanders' last home game at this level.
He will not discuss the future until the campaign ends but he and assistant Glenn Pennyfather are tipped to take over at Ryman Premier Chelmsford City.
King's decision was prompted by poor attendances at Park Lane and here, despite the boost of over 100 visiting fans, the attendance was only 641.
Canvey could have been in trouble on four minutes when Jamie Mackie robbed Steve Ward but fortunately for the home side the shot from Lee Phillips was straight at goalkeeper Danny Potter.
The Islanders forced a couple of corners that came to nothing, but the Grecians were dangerous again on eight minutes when midfielder Jon Challinor fired just wide.
A 13th minute Billy Jones free-kick from the right was turned round a post by Potter. A great run by home midfielder Mario Noto came to nothing when striker Jason Hallett held onto the ball too long before shooting.
On a sunny and fairly warm afternoon the clash between two sides with little to play for had a real end of season feel about it.
There was little significant action in either goalmouth until the 37th minute when Mackie beat Potter to a throughball but Ward rescued the situation with a timely clearance.
At the other end John Keeling sent over a dangerous cross from the left and goalkeeper Martin Rice punched clear at the near post.
Keeling was providing most of the danger when Canvey did launch attacking raids and, from another of his left-wing crosses on the stroke of half-time, Dwain Clarke was wide of the far post with a header.
But generally it had been an undistinguished opening 45 minut6es
As the second-half got underway Keeling again threatened on the left and his 57th minute cross saw Clarke send in a shot that Jones blocked.
And a minute later the visitors looked set for the lead but Potter did superbly to turn Challinor's header from Andy Taylor's right-wing cross wide.
Then home full-back Stuart Bimson's bid to try and chest the ball back to Potter nearly came unstuck as Taylor nipped in and was only just wide.
Canvey had a half-chance when Grecians goalkeeper Rice failed to deal with a Jeff Minton corner from the left, but defender Ben Chenery shot wildly off target.
Rice was forced to turn a deep cross from the right away under pressure from substitute Neil Gregory.
Another arrival from the Canvey bench, transfer-seeking Boylan, was just wide with an attempted lob but, with seven minutes to go, the game was petering out to an undistinguished goalless draw.
But all that changed in the 84th minute when a good passing movement saw Matthew Gill, who'd enjoyed a good game in the visiting midfield, put full-back Jones in for an 18-yard shot that hit the far corner of the net.
Only another fine save from Potter, to keep out a close-range Phillips effort after Challinor's shot had been blocked, saved Canvey from going 2-0 down after 87 minutes.
Canvey forced a late corner which saw Rice hold a drive from Jay Conroy well.
But they grabbed a point when Boylan scored from close range when Potter knocked the ball forward from a 90th minute free-kick.
The striker did superbly to turn a volley home as he was falling to score his 13th goal of an injury-plagued season.