He had not expected her to be able to repel his spell, especially when he was off his balance (bloody knee), though a part of him was grateful that she wasn't harmed. She might be a muggle lover but she was his sister in law, had been his fiancee for a few weeks even, he really did not want to duel her.
That did not solve the problem of him moving too slowly, however. As much as he tried to toss himself to the side, he was too slow, and he ended up misjudging the direction of the spell.
The slashing hex ended up hitting him square in the gut, drawing a scream from him as he slashed through the soft tissue and creating a deep gash that bleed thick and dark. He fell, his vision blackening and he tried to draw breath enough to heal himself, only he was loosing blood too fast, too much, and from the looks of it his liver was slashed too. Possibly more or his organs. He collapsed next to Tiberius dead body, his heart slowing with every beat.