Why is Bd3 a blunder?

Two rounds have been played at the London Chess Grand Prix. Hikaru Nakamura lost his game in the first round, but had Rustam Kasimdzhanov gift him this game in the second round. (Read the reports on Chess Blog.) White has just played 60.Bd3. Can you spot why it is a blunder?

Indeed, 60.Bd3 leads to checkmate in two! 60.Bd3 Rd2+ 61.Ke1 Rc1 0-1 Here is the full game in the Chess King applet.

Kasimdzhanov Rustam – Nakamura Hikaru

Result: 0-1
Site: FIDE Grand Prix
Date: 2012.09.22
[…] 1.d4 ¤f6 2.c4 g6 3.¤c3 ¥g7 4.e4 d6 5.¤f3 O-O 6.¥e2 e5 7.O-O ¤c6 8.d5 ¤e7 9.¤e1 ¤d7 10.¥e3 f5 11.f3 f4 12.¥f2 g5 13.¦c1 ¤g6 14.¤b5 b6 15.b4 a6 16.¤c3 ¦f7 17.¤d3 h5 18.c5 bxc5 19.bxc5 ¥f8 20.cxd6 ¥xd6 21.¤a4 ¤f6 22.¤dc5 ¦g7 23.¤e6 ¥xe6 24.dxe6 £e7 25.¤c5 ¢h8 26.¤b7 ¥a3 27.¦c3 ¥b4 28.¦d3 £xe6 29.£b3 £xb3 30.¦xb3 a5 31.¦c1 g4 32.¢f1 g3 33.hxg3 fxg3 34.¥xg3 h4 35.¥f2 ¤h5 36.f4 ¤hxf4 37.¥g4 ¦f8 38.a3 ¥d6 39.¤xa5 ¤e7 40.¥f3 h3 41.gxh3 ¤xh3 42.¢e2 ¤g5 43.¤c4 ¤g6 44.¦h1+ ¢g8 45.¤d2 ¤f4+ 46.¢d1 ¦a8 47.¤c4 ¦a4 48.¤xd6 cxd6 49.¦h6 ¦f7 50.¦xd6 ¤fh3 51.¢e2 ¦c4 52.¥b6 ¦c2+ 53.¢d1 ¦h2 54.¥e2 ¤xe4 55.¦d8+ ¢g7 56.¦e3 ¤hg5 57.a4 ¦f6 58.¦d7+ ¢g6 59.a5 ¦c6 60.¥d3 ¦d2+
and it’s mate next move: 61…Rc1 mate.