Kaley Cuoco and Johnny Galecki are ''just the best of buds.''

The 'Big Bang Theory' actress has laughed off rumours she is having a ''secret fling'' with her co-star and on-screen love interest, who she also once dated in real life for two years, following her recent split from estranged husband Ryan Sweeting.

The 29-year-old star addressed the speculation on Instagram by sharing a photograph of her and Johnny smiling widely and fist bumping, with the caption: ''So sorry to disappoint, but no home wreckers or secret flings going on here. Me and @sanctionedjohnnygalecki are just the best of buds - Leonard and Penny will just have to suffice!!!''

The 40-year-old actor also posted a similar photograph on his profile, with the caption: ''No scandals / home wreckers / pregnancies here, y'all. Just profound friendship. @normancook (sic).''

The sitcom star and Ryan, 28, announced their separation on September 25 after just 21 months of marriage.

The pair tied the knot on December 31, 2013, after dating for just six months.

Kaley allegedly ended their romance after he became ''addicted to painkillers''.

Her co-star Mayim Bialik recently insisted she is doing well despite the drama.

She said: ''Kaley's amazing. She has amazing friends, she has amazing family.

''We love her to pieces and we give her as much joy and laughs as we give everybody who sees the stuff that we do but she gets to experience it off camera.''